Historically, many fluoroalkyl surfactants were based on the perfluoroalkylethanols, F(CF2CF2)qCH2CH2OH, the so-called “Telomer B alcohols”, where q was typically about 2 to 10. The Telomer B alcohols and their preparation are described by Kirchner et al. in U.S. Pat. No. 5,202,506. Other fluoroalkyl surfactants based on Telomer B alcohols have included “twin-tailed” anionic surfactants such as F(CF2CF2)q(CH2CH2)OCOCH2CH(SO3Na)COO(CH2CH2)(CF2CF2)qF, where q is as defined above, prepared by firstly reacting two moles of one or more perfluoroalkylethanols with one of maleic anhydride and, secondly, reacting the diester product with sodium hydrogen sulfite solution, as described, for instance, by Yoshino et al. in “Surfactants having polyfluoroalkyl chains. II. Syntheses of anionic surfactants having two polyfluoroalkyl chains including a trifluoromethyl group at each tail and their flocculation-redispersion ability for dispersed magnetite particles in water”, Journal of Fluorine Chemistry (1995), 70(2), 187-91. Yoshino et al. reported examples wherein q was 2, 3, and 4 for use in supercritical carbon dioxide. Yoshino et al. report twin-tailed surfactants wherein both end groups are limited to perfluoroalkyl groups.
Nagai et al. in US Patent Application 2008/0093582, describe twin-tailed surfactants of the structureRf—(CH2)n1—(X1)p1—CH(SO3M)(X2)q1—Rh wherein Rf is a fluoroalkyl group that may contain an ether bond, X1 and X2 are the same or different divalent linking groups; M is H, an alkali metal, half an alkaline earth metal, or ammonium; Rh is an alkyl group; n1 is an integer of 1 to 10; and p1 and q1 are each 0 or 1.
One common route to perfluoroalkylethanols used to make such surfactants is a multi-step process using tetrafluoroethylene. Tetrafluoroethylene is a hazardous and expensive intermediate with limited availability. It is desirable to provide fluorinated surfactants that use less or no tetrafluoroethylene in their preparation.
It is also desirable to provide new and improved fluorinated surfactants in which the perfluoroalkyl group of the prior art is replaced by partially fluorinated terminal groups that require less tetrafluoroethylene and show increased fluorine efficiency. By “fluorine efficiency” is meant the ability to use a minimum amount of fluorochemical to obtain a desired surface effect or surfactant properties, when applied to substrates, or to obtain better performance using the same level of fluorine. A polymer having high fluorine efficiency generates the same or greater level of surface effect using a lower amount of fluorine than a comparative polymer. The present invention provides such improved fluorinated surfactants.